Chancroid is a human sexually transmitted disease caused by Haemophilus ducreyi and characterized by painful genital ulcers. The primary ulcer is often followed by multiple lesions which result in ulcers of various ages that can extend the duration of the illness to 1 to 3 months if appropriate treatment is not given (37). More than 50% of the cases progress to inguinal lymph node involvement manifested by buboes(37). Without treatment, the bubo can persist for many months. Infections with other pathogens such as Treponema pallidum, herpes simplex virus type 2, Chlamydia trachomatis (lymphogranuloma venereum), and Calymmatobacterium granulomatis (granuloma inguinale) can result in ulcerations clinically indistinguishable from those caused by H. ducreyi. Thus, accurate diagnosis of the etiologic agent is very important, since antimicrobial treatment for those different sexually transmitted diseases must be specific.
Open chancroidal lesions may enhance transmission of human immunodeficiency virus. Recent studies in Africa have established a significant association between history of genital ulceration and human immunodeficiency virus seropositivity (24, 30, 35). Since chancroid has been reported to be the most common cause of genital ulcers in Africa (12), this disease has been correlated specifically with heterosexual transmission of human immunodeficiency virus (35). These studies, together with the clinical observation that untreated ulcers can persist for months, highlight the importance of an accurate diagnosis which will lead to appropriate therapy.
H. ducreyi is a fastidious, slow-growing, gram-negative bacillus. Colonies grown on solid media vary in size, perhaps because of the peculiar cohesiveness of the organism, with larger colonies arising from more than one cell. Moreover, H. ducreyi remains tightly autoagglutinated when suspended in liquid. This cohesiveness has ruled out identification of the organism by serological agglutination tests, and difficulties in interpretation of fluorescent-antibody tests (due to bacterial clumping) have also been reported with both polyclonal (14) and monoclonal antibodies (33).
To maintain viability of the bacteria, H. ducreyi must be cultured within 4 to 6 hours after removal from the patient. Even when inoculated immediately, the organism does not grow well on most laboratory media, and recovery rates for clinical specimens have traditionally been poor. In 1978, Hammond et al. (19) reported the development of a selective enrichment agar. Use of this medium or adaptations of it (36) have led to significantly higher recovery rates of H. ducreyi in recent years. However, isolation rates of only 60 to 70% are still the norm for patients with clinically diagnosed chancroid (26).
During the past decade, outbreaks of chancroid have been reported in both Canada and the United States (3, 4, 8, 9, 20, 21, 27). In New York City, outbreaks have been reported yearly, beginning in 1981 (10) and the number of cases has been increasing each year since then. In 1987, over 62% (3,116 of 4,998) of the chancroid cases reported in the United States were from New York City (11).
In summary, the increasing incidence of chancroid is a matter of serious concern not only because of the problems of chancroidal disease itself, but also because this disease has been associated with heterosexual transmission of human immunodeficiency virus in Africa. Difficulties in clinical and laboratory diagnosis can interfere with an accurate identification of chancroid or its etiologic agent.
DNA probes for the detection of microorganisms, particularly Legionellas, have been described in the literature. (38) These compositions are obtained from the whole genomes of Legonella pneumophila, which are fragmented by a restriction endonuclease, and from these fragments are eliminated those sequences which are susceptible to being transcribed to ribosomal RNA.
Other methods which may be useful for the detection of H. ducreyi also have been disclosed. These methods, however, do not utilize specific DNA probes. One such method uses protein binding assays as the method of detection. (39) Another method uses monoclonal antibodies. (40)